Go to Calendar.
Select the Calendar tool from the Tool Menu in your site.
Choose Add/Edit Fields.
To add a new field:
Enter the Field Name into the text box provided.
Select the Create Field button.
The new field will now display in the list of existing fields on this page. It will also show up as a field for each calendar event when you add or edit an event.
To delete an existing field:
Select the check box next to the field or fields you would like to remove.
Select the Remove selected fields button.
The removed field will no longer display in this list, or on the calendar event details screen.